Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with transitional graphical user interface showing our new design in a first state;

FIG. 2 is a front view thereof shown in a second state; and,

FIG. 3 is a front view thereof shown in a third state.

The numbers (12:45) shown in light gray solid lines in FIG. 2 form part of the claimed design.

The broken lines in the figures depict environmental subject matter and form no part of the claimed design.

The outermost broken lines in the figures show a display screen or portion thereof and form no part of the claimed design.

The appearance of the transitional graphical user interface sequentially transitions between the images shown in FIGS. 1-3. The process or period in which one image transitions to another forms no part of the claimed design. 

CLAIM We claim the ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 